(a) Field of the Invention
The present invention relates to a transflective (transmissive-reflective) liquid crystal display (LCD).
(b) Description of the Related Art
Generally, an LCD includes a pair of panels individually having electrodes on their inner surfaces, and a dielectric anisotropy liquid crystal (LC) layer interposed between the panels. In an LCD, a variation of the voltage difference between the field generating electrodes, i.e., a variation in the strength of an electric field generated by the electrodes, changes the transmittance of the light passing through the LCD, and thus desired images are obtained by controlling the voltage difference between the electrodes.
Depending on the kinds of light source used for image display, LCDs are divided into three types: transmissive, reflective, and transflective (transmissive-reflective). In transmissive LCDs, pixels are illuminated from behind using a backlight. In reflective LCDs, the pixels are illuminated from the front using incident light originating from the ambient environment. The transflective LCDs combine transmissive and reflective characteristics. Under medium light conditions such as an indoor environment, or under complete darkness conditions, these LCDs are operated in a transmissive mode, while under very bright conditions, such as an outdoor environment, they are operated in a reflective mode.
In the transflective LCDs, two absorbing polarizers, each of which is a film obtained by adding iodine molecules or bichromatic dyes to stretched PVA, are individually attached to the outer surfaces of the panels. The absorbing polarizers exhibit some unique optical characteristics. In detail, they allow only P-waves of incident light to pass, and absorb S-waves. Theoretically, an absorbing polarizer transmits 50% of the incident light and absorbs the remaining 50%. Practically, however, the absorbing polarizer transmits only 43% to 45% due to a light loss occurring at its surface.
In a transflective LCD, there are transmission areas and reflection areas. Light entering the reflection areas of the LCD from a backlight unit is returned toward the backlight unit by reflection at reflective electrodes. At this time, most of the light is removed by absorption at the absorbing polarizer.
Due to such an absorption light loss, light efficiency and display luminance of the LCD are less than optimal.